The use of telecommunications devices by businesses and other facilities has expanded rapidly in recent years. Most businesses today employ, e.g., one or more telephone sets, facsimile machines, telephone answering machines and modems.
In order to reduce the cost of providing telephone service for all such devices, apparatuses have been developed for enabling telecommunications devices to share telephone lines. One such apparatus enables a modem, telephone set and facsimile machine to share a single-subscriber telephone line. As used herein, a single-subscriber telephone line means a telephone line normally connected to a single telecommunications device and to which the public telephone network normally assigns a single telephone number. This apparatus answers an incoming telephone call and then directs the call, based upon the signals transmitted by the calling device after doing so, to the telephone set, modem or facsimile machine. The signals transmitted by such devices, after establishing a connection to a called device, all have characteristic indicia. By identifying these indicia, the apparatus identifies the telecommunications device to which the call should be directed. After making this identification, the apparatus generates, and transmits to the identified telecommunications device, a ringing signal. If this telecommunications device answers the ringing signal, the apparatus then makes a connection between this telecommunications device and the telephone line. Examples of such telephone line sharing apparatuses are disclosed in U.S. Pat. Nos. 4,584,434; 4,660,218; 5,151,972 and 5,187,736.
Such telephone line sharing apparatuses, however, are unable to provide telephone line-sharing for a plurality of telecommunications devices of the same type. Also, with such telephone line sharing apparatuses, additional time is required to complete a telephone call. The apparatus must answer the telephone call, determine the telecommunications device to which the telephone call should be directed, and then must transmit a ringing signal to this device.
Manual switch boxes also can be used to provide telephone line sharing. A telephone line is connected to one side of the box, and two or more telecommunications devices are connected to the other side of the box. The box's switch is set to provide a connection between one of the telecommunications devices and the telephone line. In order to provide a connection between another of the telecommunications devices and the telephone line, the switch must be manually reset.
A modem connected to a computer network also can provide telephone line sharing for computers on the network. The modem answers incoming telephone calls and directs these calls to one of the network's computers, in accordance with instructions received from the network's operating system. A computer seeking to make an outgoing data transmission transmits a request over the network to the modem. If the modem is available, a connection then is made between the modem and this computer for making the outgoing transmission.
A private branch exchange (PBX) also provides telephone line sharing. A PBX employs multiplexing techniques and is used as an interface between the public telephone network and a large business or other such facility. The PBX answers incoming telephone calls and then directs these calls to telecommunications devices connected to the PBX in accordance with a protocol executed by a controller. Ringing signals, generated by the PBX, are transmitted to the telecommunications devices for completing the cells.